Drive apparatus



Nov. 10, 1959 G. R. MITCHELL 2,911,843

DRIVE APPARATUS Filed Jan. 26, 1959 INVENTOR. George R;Mitchell BYflmjmmd M%/ ATTORNEYS United States Patent DRIVE APPARATUS George R.Mitchell, Homewood, Ill., assignor to Sinclair Refining Company, NewYork, N.Y., a corporation of Maine Application January 26, 1959, SerialNo. 789,023

Claims. (Cl. 74-361) This application is a continuation-in-part of mycopending application, Serial No. 630,257, filed December 24, 1956.

My invention relates to valve actuation and in particular provides anelectromechanically actuated valve.

With the advent of control systems employing electric current ratherthan compressed air and hydraulic fluid as a control medium there hasbeen an interest in replacing diaphragm valve actuators and the likerequiring compressed air or hydraulic fluids for operation with deviceswhich rely solely on electromechanical actuation.

It is therefore a principal object of my invention to provide anelectromechanically actuated valve suitable for remote operation by aninput electrical control signal which can be manually selected or whichcan be determined by a control instrument developing an electric output.

It is a further object of my invention to provide a valve having abi-directional rotating drive developing a high torque to energy ratiocomparable to linear thrust developed by conventional pneumatic andhydraulic controls.

It is still a further object of my invention to provide such a valvesuitable for operation by an electric control system and capable of highpositioning accuracy, minimizing overshooting, simple error and phasedetection, and essentially flat frequency response.

These and other objects of my invention, which will become apparenthereinafter, are basically achieved with a rotatively actuated valvewhich is connected to a continuously operating electrical motor by apair of transmissions each of which includes an electromagnetic clutchand which are connected to the valve opposing each other such thatactuation of one clutch will tend to displace the valve stem in onedirection to close the valve and actuation of the other clutch will tendto displace the valve stem in the opposite direction to open the valve.A closed loop, automatic feedback system is employed to control theposition of the screw driven valve stem through such bi-directionaldrive responsive to the deviation between the position of the stem andan input electrical control signal. In a more particular aspect thecontrol system also includes means for damping the movement of the valvestem as it approaches a desired position. Such damping can be ratedamping responsive to the rate of rotation of the valve stem actuator tocontrol the speed of the correcting movement of the valve stem as thevalve approaches the desired position. Alternatively, damping can befurnished by an anticipating device operative when the valve stemactuator rotates to decontrol the position feedback system just prior tothe valves reaching the desired position.

For a more complete understanding of the practical application for theprinciples of my invention reference is made to the appended drawingwhich is a diagrammatic illustration of an electromechanically actuatedvalve having a bi-directional drive and employing an electrical controlsystem utilizing both position feedback and 2 damping in accordance withthe principles of my invention.

In the drawing the reference numeral 10 indicates a slide valve, theposition of which is operated by bi-directional drive 11 controlled byan electrical control system 12, including an error detector 13, anamplifier 14 and an error corrector control 15, for developing acorrecting signal governing the operation of bi-directional drive 11.

Valve mechanism 10 includes a housing 20 connected at one end to aconduit 21 and connected at the other end to a conduit 22. Withinhousing 20 is located a valve element 23 which is reciprocabletransversely of the ends of housing 20 to control the passage of fluidsbetween conduits 21 and 22. A valve stem 24 which extends slidablythrough a fluid-tight bushing 25 into housing 20 is afiixed to valveelement 23, and hence, longitudinal movement of stem 24 causes element23 to slide across the interior of housing 20 in one direction or theother to open or close valve 10.

Valve stem 24 externally carries a flanged collar 26 and is received inthreaded engagement by a gear 27 which is operated by bi-directionaldrive 11.

Bi-directional drive 11 includes a continuously operable A.C. motor 30,the output shaft 31 of which carries a pinion 32 which meshes with agear 33. Gear 33 also meshes with a gear 34 in 1:1 ratio such that theoutput shafts 35 and 36, respectively driven by gears 33 and 34, arecounterrotating at the same speed. Shafts 35 and 36 are respectivelyconnected to the input sides of electromagnetically actuated frictionclutches 37 and 38, the output sections of which respectively driveshafts 39 and 40 which respectively carry pinions 41 and 42 each ofwhich meshes with gear 27 carried on valve stem 24. Thus, when motor 30is continuously operating, actuation of clutch 37 causes gear 27 torotate in a direction tending to open valve element 23 and similarlyactuation of clutch 38 causes valve stem 24 to move in a directiontending to close valve element 23.

Error detector 13 includes a position feedback device 45, a referencingdevice 46 having input terminals 47 and 48 for connection to a manuallyor instrumentally operated control signal, a differential transformer 49and a preamplifier 50.

More specifically position feedback device 45 includes a lever 51pivotally mounted at its center on a fixed pin 52 and having a forkedend 53 received by collar 26 between the end flanges of collar 26 suchthat vertical movement of valve stem 24 produced by rotation of gear 27,will cause lever 51 to pivot about pin 52. A second lever 54 pivotallymounted on its center on a fixed pin 55 is pivotally connected at oneend to one end of a link 56 which is also pivotally connected at itsother end to the end of lever 51 remote from fork 53. At its other endlever 54 is connected through a tensed coil spring 57 to a balance arm58 which is also pivotally supported near its center as indicated by thereference numeral 59.

At its end opposite spring 57 balance arm 58 carries a ferro-magneticcore 60 arranged such that movement of arm 58 about pivot point 59 willcause core 60 to move into and out of differential transformer 49. Arm58 also carries at the same end as coil spring 57 a pair offerro-magnetic cores 61 and 62 which are slidably received as cores in apair of coils 63 and 64 connected in series across input terminals 47and 48. Thus the position of core 60 in transformer 49 is a function ofthe input signal connected across terminals 47 and 48 and of theposition of valve element 23.

The primary winding 65 of transformer 49 is supplied with alternatingcurrent; and accordingly, since the output windings 66 and 67 areconnected out of phase by lines 68 and 69 to preamplifier 50, the outputof preamplifier 50 is an electrical signal which is a function of thesame difference in inputs and thus is an error signal which can beutilized to cause valve 23 to assume a specific position for any giveninput signal at terminals 47 and 48 which will produce a zero errorsignal output from preamplifier 50.

Amplifier 14 which suitably includes thermionic vacuum tube triodecircuits in one arrangement is supplied both with an input error signal(the output of preamplifier 50) as indicated by line 70 and a ratefeedback input via line 71 derived from an AC. tachometer generator-72the armature of which is connected to drive shaft 39 such that theoutput voltage tapped from secondary winding 73 by line 71 is a functionof the speed of rotation of gear 27 and accordingly of the speed ofmovement of valve element 23. The primary winding 74 of generator 72 issuitably supplied with alternating current in series with a capacitor75.

Amplifier 14 suitably is constructed such that the rate feedback signalsupplied via line 71 biases one or more of the vacuum tubes in theamplifier thus controlling amplification of the error signal introducedvia line 70 as a function of the speed of valve element 23 by drivingthe amplifier tubes past cut-01f bias when the speed of gear 27 exceedssome preselected rate. The net correcting signal output of amplifier 14is fed via line 76 to error corrector control system 15 which functionsas a phase detector supplying current via line 77 to energize clutch 37when the error signal developed by detector 13 indicates the differencebetween the control signal supplied across input terminals 47 and 48 andthe position of valve element 23 demands that valve element 23 befurther opened. Conversely error corrector 15 energizes electricmagnetic clutch 38 via line 78 when the difference between the signalapplied to input terminals 47 and 48 and the position of valve element23 demands that valve element be further closed.

Thus in operation terminals 47 and 48 are suitably connected to areference potential source such as the movable tap 80 of a potentiometer81 connected across a DC. power supply 82. Since the position of core 60represents a balance between the force exerted by spring 57 and themagnetic force produced by passage of current through coils 63 and 64,it will be apparent that for every setting of tap 80 there will be acorresponding position of valve element 23 in which the control systemis balanced and the error signal is zero. Starting in such a balancedstate, if tap 80 is moved to decrease the potential applied to terminals47 and 48, arm 58 will revolve a short distance counter clockwiseproducing an error signal in the output of transformer 49, whichpreamplified at 50, amplified at 14 and detected at 15 will energizeclutch 37. It should be observed that motor 30 is constantly rotatingand thus gears 33 and 34 are also rotating counter to each other. Theenergization of clutch 37 couples shafts 35 and 39 causing gear 27 torotate in a direction raising valve stem 24 to open valve element 23 andat the same time decreasing through linkage 45, the tension on spring 57tending to restore core 60 to a balanced, Zero error signal position. Asgear 27 begins to turn at an increasingly faster rate the output oftachometer generator 72 increases the bias on amplifier 14 past cut-01funtil no error signal appears in line 76 whereupon clutch 37 isde-energized. Decoupled gear 27 then decelerates until the output ofgenerator 72 is decreased sufficiently for the error signal to overcomethe cut-01f bias of amplifier 14. The error signal in line 76 is thenrestored and clutch 37 is again energized. It will be evident that largeerror signals will overcome greater biases on amplifier 14 than smallerror signals, and hence pecking action of error corrector 15 can becontrolled such that overshooting is held to a minimum and efiectivedamping of the movement of valve element 23 is achieved.

In another suitable arrangement in accordance with my invention insteadof supplying rate feedback to amplifier 14 to control the speed ofmovement of valve stem 24, a small portion of feedback signals fromtachometer generator 72 is connected as an input at a stage of amplifier14 where the error signal is of considerably larger magnitude than theportion of the feedback signal derived from tachometer generator 72 suchthat the latter bucks the error feedback. Thus, damping control of thecorrecting movement is no longer based on driving the amplifier tubespast cut-01f bias. Accordingly, gear 27 will assume a constant speedsince the clutch 37 or 38 through which gear 27 is connected to motor 30remains energized until the error signal fed to amplifier 14 reaches avery small value at which the bucking feedback signal from generator 72cancels the error signal. At such point the clutch 37 or 38 which wasenergized will be de-energized, and gear 27 and valve stem 24 will stopmoving, stopping the movement of valve element 23. The amount of thetachometer generator 72 output fed to amplifier 14 is adjusted such thatthe coasting of gear 27 and valve stem 24 to stopped position from theirnormally constant rate of movement will carry the valve element 23 theprecise distance required to reach the desired position. Sinceordinarily the same constant rate of rotation of gear 27 will occur inany correctional movement required by the control system, one adjustmentof the amount of tachometer generator 72 feedback to a correct value atwhich valve stem 24 coasts to a stop exactly at the desired positionwill ordinarily be all that is required.

I claim:

1. In a valve including a longitudinally movable operator therefor andactuating means for said operator rotatably cooperating therewith, theimprovement which comprises a first power transmission means including afirst electromagnetically actuated clutch, a second power transmissionmeans including a second electromagnetically actuated clutch, said firstand second transmission means being separately connected to saidactuating means to rotate said actuating means, drive means connected toeach of said first and second power transmission means whereby saidactuating means is rotated in one direction by said first transmissionmeans when said first clutch is actuated and in the opposite directionby said second transmission. means when said second clutch is actuated,and control means for selectively actuating said first and secondelectromagnetic clutches, said control means including a positionsensitive device connected to said operator and having an outputresponsive to the longitudinal position of said operator, and a secondsensitive device connected to said actuating means having an outputresponsive to the rotation thereof.

2. In a valve including a longitudinally movable op erator therefor andactuating means for said operator rotatably cooperating therewith, theimprovement which comprises a first power transmission means including afirst electromagnetically actuated clutch, a second power transmissionmeans including a second electromagnetically actuated clutch, said firstand second transmission means being separately connected to saidactuating means to rotate said actuating means, drive means connected toeach of said first and second power transmission means whereby saidactuating means is rotated in one direction by said first transmissionmeans when said first clutch is actuated and in the opposite directionby said second transmission means when said second clutch is actuated,and control means for selectively actuating said first and secondelectromagnetic clutches, said control means in cluding a positionsensitive device connected to said op erator and having an outputresponsive to the longitudinal position of said operator, and a ratesensitive device connected to said actuating means and having an outputresponsive to the rate of rotation thereof.

3. The improvement according to claim 2 wherein said control mcans,selectively actuates said first and second electromagnetically actuatedclutches in response to a difference between the output of said positionsensitive device and an input reference signal at a rate responsive tothe output of said rate sensitive device to drive said operator to aposition in which the output of said position sensitive device equalsthe input reference signal.

4. The improvement according to claim 2 wherein said position sensitivedevice further comprises an electromagnetic referencing device includinga balance arm, spring means mechanically connected to said operator andsaid balance arm to exert a force on said arm responsive to longitudinalposition of said operator, means for electromagnetically coupling aninput reference signal to said arm to exert a force on said armresponsive to said input reference signal, and a differentialtransformer responsive to the position of said arm for generating anoutput signal.

5. In a valve including a longitudinally movable operator therefor andactuating means for said operator rotatably cooperating therewith, theimprovement which comprises a first power transmission means including afirst electromagnetically actuated clutch, a second power transmissionmeans including a second electromagnetically actuated clutch, said firstand second transmission means being separately connected to saidactuating means to rotate said actuating means, drive means connected toeach of said first and second power transmission means whereby saidactuating means is rotated in one direction by said first transmissionmeans when said first clutch is actuated and in the opposite directionby said second transmission means when said second clutch is actuated,and control means for selectively actuating said first and secondelectromagnetic clutches, said control means including a positionsensitive device connected to said operator and having an outputresponsive to the longitudinal position of said operator, and a secondsensitive device connected to said actuating means and having an outputresponsive to the rotation thereof, said control means selectivelyactuating said first and second electromagnetically actuated clutches inresponse to a difference between the output of said position sensitivedevice and an input reference signal to drive said operator toward aposition at which the output of said position sensitive device equalsthe input reference signal, and said control means selectivelydeactuating said first and second clutches in response to said output ofsaid second sensitive device at a position of said operator approachingsaid position thereof at which the output of said position sensitivedevice equals the input reference signal.

No references cited.

